1. Field of the Invention
This invention relates generally to shaft seals and more specifically to a shaft sealing device having a pressure balanced floating housing.
2. Description of Prior Art
Shaft packing has been used on submarines since World War II. The nuclear powered submarines have larger shafts and operate at greater depths and development efforts have concentrated exclusively on mechanical face seals. The recent nuclear submarines have had still larger shafts. Unfortunately, the mechanical face seals are expensive and have to be replaced often due to wear and corrosion problems. They are becoming very heavy and costly in the larger sizes and have some problems with distortion under pressure, manufacturing tolerances and secondary "O" ring seal support for the seal ring. Some of the problems can be overcome by new configurations and more costly materials. The seals require very careful experienced mechanics to assemble the split configuration over the shaft and there is no assurance that the surface dimensions are acceptable after assembly.
The concept of using packings for shaft sealing has been in use for a long time. Their usefulness has been greatly limited by their inability to perform at elevated pressures and at high shaft surface velocities (without burning up), and an inability to be adaptable to radial shaft motions. Recently, packing materials have become available that offer higher temperature capabilities, lower coefficients of friction, greater strand tensile yields (better protection against packing degradation), and lower wear.
The successful operation of packings requires that the gap between the shaft and housing be small. This prevents excessive extrusion of the packing or even blowout of the seal. The small gap however prohibits any appreciable shaft radial motion; excessive motion would result in eventual shaft damage. This requirement prevented the use of packings for large shaft operation, where radial shaft motion is unavoidable, or where shock loadings would be encountered.